Hydrocarbon refining to reduce sulfur, nitrogen, and naphthenic acid content



April 1961 A. c. VAN BEEST ET AL 2,980,606

HYDROCARBON REFINING TO REDUCE SULFUR, NITROGEN AND NAPHTHENIC ACIDCONTENT Filed Aug. 12, 1957 2| COALESCER 38 22 50 'T/COALESCER SETTLER,3 A 24 l, SETTLER GosOH I \29 R SETTLER 40 MIXER Sulfuric 25 Acid 42 a329 as Acid Make-up Gus 0il J 72 SALT T 48 COALESCER T 6 S'g- 57 '58G050" I I GusOil 46 SETTLER T R 63 SETTLER MIXER SE TLE MIXERBicorbqnufe Soluhon water WOLL 5o 52 r I 66 7| Bicarbonate so" Make-upSolution INVENTORSI ADOLF CHRISTIAAN VAN BE'EST JACOBUS WILHELMUS LENOBEL BY: 0&JR W

ATTORNEY United States Patent HYDROCARBON REFINING TO REDUCE SULFUR,

NITROGEN, AND NAPHTHENIC ACID CON- Filed Aug. 12, 1957, Ser. No. 677,434Claims priority, application Netherlands Aug. 14, 1956 4 Claims. (Cl.208-254) The presentinvention relates to the treatment of petroleumhydrocarbons andmore particularly pertains to an improved method for therefining of hydrocarbon materials to reduce their naphthenic acidcontent.

Various crude oils, as for example, certain Venezeula,

Trinidad, California, and Borneo crude'petroleums contain minor amountsof naphthenic acids. In the processing of these crudes or theirdistillates, it is conventional practice to wash the crude oil orpetroleum fraction with an aqueous alkali solution in order to separatethe naphthenic acids in the, form of water-soluble soaps from thehydrocarbons. Since the naphthenic acids and their salts are valuableindustrial materials, the dissolved naphthenates are then usuallyacidified to permit their recovery from the alkali wash water. Thenaphthenic acids and their salts are used, among other purposes, ascomponents in paint formulations, detergents, and for making varioufungicidal compositions.

.The foregoing alkali washing of the crude oil or petroleum fractiondoes not extract all of the naphthenic materials from the oil and traceamounts of the naphthenates remain behind, dissolved in the oil wherethey mayand do frequently cause difficulties. For instance, when the oilcomes into contact with water, as is likely to occur during transport,the trace naphthenates together with the water cause a very persistentturbidity in the oil, so-called permanent haze. It is also known thatsmall amounts of thesoap present in diesel fuel oils may result ininjector and filter plugging. In addition,.

simple alkali washing of the petroleum fraction may be attended byserious emulsion troubles which are traceable to the entrainment of thealkali and. of the naphthenate soaps in the oil being treated. Suchemulsions are, of course, undersirable and will frequently necessitatefurther refining to assure their removal.

Methods have been suggested for preventing the emulsification and forreducing naphthenate soap entrainment in the treated petroleumfractions. It is known, for instance, that the foregoing .difiicultiesmay be appreciably lessened, by treating the petroleum oil or fraction.with an alkali solution containing not only say free alkali metalhydroxide but also the reaction products of that material with 'weakorganic acids. These weak organic acids may be, among others, phenol,alkyl phenols, thiophenols, alkyl thiophenols, fatty acids such asisobutyric or naphthenic acids having lower average molecularweightsthan the naphthenic acids present in the 'oil' being treated. Thealkali metal hydroxide solution containing the above reaction productmay be readily preparedby first treating a hydrocarbon oil which hasa'lower boiling range than the oil to be processed with an alkali metalhydroxide solution. The latter solution extracts phenols, thiophenols,low molecular weight naphthenic acids, etc. from the lower boilinghydrocarbon oil, thus providing an alkali solution especially adapted tothe treatment of the heavier hydrocarbon oil. The. foregoingreactionprodnets of the alkali and weak organic acids are sometimesdescribed as solutizers for the naphthenates. If convenient, thereaction products of the alkali metal hydroxide I and the organic acidmay be prepared separately and then added to the alkali metal hydroxidesolution.

However, even with the use of a solutizer in the caustic solution usedfor neutralizing and extracting the naphthenic acids, the caustictreated petroleum fraction will still frequently contain trace amountsof naphthenates which cause haziness. Moreover, oils treated withcaustic solutions containing a solutizer possess an offensive odor.

The trace naphthenic soaps present in the treated oil may be acidifiedwith sulfuric acid, thus placing the naphthenates in their acid formwhich will obviate the problem of turbidity. However, the acid treatedoil may be corrosive to metals, especially copper and zinc. If, in orderto avoid corrosion difi'iculties, less than a stoichiometric amount ofsulfuric acid is employed to wash the caustic treated oil, the problemof haze remains to the extent that the naphthenates are present.Therefore, from a practical standpoint, an excess of sulfuric acidshould be employed.

It is an object of this invention to provide an improved method oftreating a hydrocarbon oil which contains naphthenic acids to obtain atreated hydrocarbon free of naphthenic soaps and essentially free ofnaphthenic acids. This and still other objects of the present inventionwill become apparent from the following description of the invention,made in conjunction with the accompanying drawing in which the solefigure shows diagrammatically a preferred system for performing theprocess of the invention.

It has now been discovered that naphthenic acid-containing petroleumhydocarbons can be caustic extracted, acidified, neutralized andwater-washed to provide a prodnot which is free of naphthenic acid soapsin amounts that causeproduct haziness in the presence of water. In apreferred embodiment of the process, the hydrocarbon is first washedwith an aqueous alkali solution thereby converting the naphthenic acidspresent in the hydrocarbon material to their water-soluble soap form.The wash mixture is separated to obtain awashed hydrocarbon phase whichwill unavoidably contain a small amount of the naphthenic acid soaps(naphthenates) and an aqueous wash phase containing the vast share ofthe naphthenic soaps. The alkali washed hydrocarbon is then treated withsulfuric acid to acidify the naphthenates therein to their acid form.Subsequently, the sulfuric acid treated hydrocarbon is washed with anaqueous basic solution, preferably of a salt of a weak acid and a strongbase, having a pH of less than 8.5 to neutralize any sulfuric acidremaining in the oil, without significantly saponifying the naphthenicacids present, thus leaving the naphthenic material in a form which willnot cause haziness when the product is subsequently contaminated withwater.

The product of the improved process is odorless, clear The initialalkali or caustic treatment of the oil may be with or withouta solutizerof the type already described.

While-sodium hydroxide is generally. used, aqueous'solu-- tions ofvarious, other-alkalies may be employed, for instance, other alkalimetal hydroxides suchaspotassium hydroxide are satisfactory. Theconcentration of the' free alkali in the wash water may vary withinquite wide limits but will generally be between approximately and 40% byweight of caustic alkali based on combined Weights. of water and thealkali. solutizer is employed, the amount of thenon-hydrolyzablereaction productof. the alkali and organic acid ma-. terials shouldexceedf5% by weightand preferably the amount of solutizer used is in.excess of of thetotal caustic alkali solution. The upper limit of theconcentration will be set by the solubility of. the solutizer in theparticular alkali solution utilized but in general not over 90%saturation is preferred.

The caustic treated hydrocarbon fraction may be processed with anundiluted sulfuric acid but preferably the acid treatment ishad with awater diluted sulfuric acid containing from 60 to 90%.v acid by weight,based on Water plus sulfuric acid. A typically suitable acid wash may behad with 80% sulfuric acid,fwhere. 500 parts of the hydrocarbon istreated with 125 parts of the diluted sulfuric acid. The proportions ofacid to oil may. vary quite widely but generally with an 80% sulfuricacid solution, 75 to 200 parts of sulfuric per 500 parts of the oil isadequate. On an undiluted sulfuric acid basis, sulfuric acid in anamount of 1 part to 3 parts of oil maybe. necessary but generally anamount of say 1 part of sulfuric acid to 5 parts of the oil issufficient. In a petroleum fraction containing a relatively smallproportion of naphthenic acid soaps, it may be adequate to employ 1 partof sulfuric acidto treat 8 parts of the oil. Whatever the proportion ofacid to oil that may be employed, the object is to acidifythe naphthenicsoapspresent in the alkali treated oil to their acid form.

After separating the oil phase andthe acid phase, the oil which will nolonger possess an offensive odor is preferably passed through acoalescer to agglomerate and separate acid particles that may remaindistributed in the oil. The coalesced acid particles are then removed.

The acid treated hydrocarbon which contains traces of sulfuric acidalong with the naphthenic acids is then subjected to treatment with anaqueous basic solution having a pH of less than 8.5 and preferably inthe range of 7.5-8.2. The aqueous basic solution is preferably preparedwith a salt of a weak acid and a strong base, for example, sodiumacetate or sodium bicarbonate at a concentration of the salt in thebasic solution of generally between l-5%v by weight. The solution isnormally used in a quantity of 10-50 parts by volume per 100 parts byvolume-of the oil being treated and maybe recycled to contact furtherquantities of the oil. The sulfuric acid solution of the preceding stepmay. likewise be recirculated. By using basic solutions of the specifiedpH only the small amount of'the mineral acid present in the oilisneutralized, leaving the. naphthenic acids formed by sulfuric acidtreatment unsaponified, with the result that the product from theaqueous basic solution treatmentdoes not exhibit a permanenthaze whencontacted with water. It maybe desirable to incorporate a small quantityof alcohol, for example, ethanol in the weak' basic wash water.

The product from the basic wash procedure may, if desired, be furtherwashed with water and then dried in a salt filter. The acid number ofthe resulting oil will normally be less than 0.1 and frequently lessthan 0.05 and the mercaptan sulfur content is generally less than 0.002%by weight.

The process may be advantageously applied to the treatment ofhydrocarbons boiling between 200 and 400 C., particularly gas oils. Italso may be used for the acid neutralization of kerosene, domestic fueloil and lubricating oil. The temperature of the various stages of theprocess is generally between -80 C. The mixing of the hydrocarbonwiththe various treating liquids may be carried out in conventionalmixing devices such as propeller mixers or centrifugal mixers.

In the instance where a.

to a pump 14. The two pumps discharge into a common line 15 which opensin turn into a propeller mixer 16.

The solutizer containing caustic solution is prepared by treating acatalytically. cracked gasoline with an aqueous sodium hydroxidesolution, containing 20% by weight of sodium hydroxide, based on thewater and. alkali. The product of the alkali treatment contains 12% byweight of free sodium hydroxide and approximately 22% by volumeof sodiumsalts of weak organic acids.

Thev gas oil caustic mixture carried by theline 15, is.

commingled with 125 parts byvolume ofa recycling caustic solutioncirculating in line17. The caustic treated,

gas oil is then admitted to thepropeller mixer 16 where the enteringstream is violently agitated to assure anadequate mixing of the causticsolutions with the gas oil..

The sodium hydroxide neutralizes substantially all of the organic acidsincluding the naphthenic acids, forming water-soluble naphthenates. Theagitatedstream leaves the mixer propeller through a line 18 which opensinto a settler 19 and here the mixture separates into an alkali extractaqueous layer and an overlying extracted hydrocarbon layer which retainsa small amount of the naphthenic soaps. But by far the vast proportionof the naphthenic soaps is dissolved in the lower aqueous wash waterphase. At the far endof the settler, remote from the point of entry ofline 18, a line 17 is provided for removing the separated alkali washwater from a quiescent zone, from where it is recycled through a pump 18disposed in the line 17 to the aforementioned propeller mixer 16. Aquantity of the recycling caustic solution equal in amount to thecaustic solution introduced through the make up line 12 is drawn offfrom the recycle line 17 through a line 19. The caustic treated gas oilwhich may still contain an appreciable amount of caustic solutiondispersed throughout it, leaves the settler 19 via a line 21 which leadstocoalescer. 22 and from there to a settling tank 24 placed. preferablyimmediately below the coalescer, in which tank a further quantityof'thev caustic solution is separated from the gas, oil and passed tothey recycle line 17 viaaline 25.

The gas oil is removed fro-m the. toplayer of the settler tank throughline 26 to a second propeller mixer 28. The alkali treated hydrocarbonflowing in the. transfer line 26 has added to it, .125 parts by volumeper hour of ggrecycled sulfuric. acid phase. supplied by a recycle lineweight, based on water plus sulfuric acid, of therecycling phase. Thehydrocarbon and sulfuric acid phase are passed in a stream to the mixer28 where they are thoroughly stirred together, acidifying thenaphthenates remaining in the hydrocarbon to oil-soluble naphthenicsoaps. From the propeller mixer 28 the mixture of oil and acid phase ispassed through a line 30 to a settler 32 where the two phases areseparated from each. other. The acid phase which forms the lower layeris continuous.- ly removed from a quiescent zone of the settler and recycled through the aforementioned line 29 and a pump 33 disposed thereinto the transfer line 16 where it joins the alkali treated hydrocarbonstream from the earlier processing. One part by volume of fresh sulfuricacid of 98% by weight is added to the recycling sulfuric phase per hourthrough a sulfuric acid make up line 34 which. is provided with a pump35. A quantity of the spent. acid phase is Withdrawn via a line 36 fromthe. recycle, line 29 to maintain the proper circulating volume. The

Sulfuric acid makes up approximately by' gas oil which may contain asignificant amount of the dispersed sulfuric acid phase is led from thetop layer of the settler 32 via a line 38 to a second coalescer 39, andthen to a settling tank 40 disposed immediately below the coalescer, inwhich tank a further quantity of the acid phase is separated from thegas oil and returned through a line 42 to the recycle line 29.

The now acid treated and alkali treated hydrocarbon is transferred fromthe settling tank 40 through a line 44 to a third propeller mixer 46.125 parts per volume per hour of an aqueous sodium bicarbonate solutioncontaming about 20 grams of sodium bicarbonate per liter is added to thetransfer line 44 through a line 45. The

bicarbonate solution and acid treated hydrocarbon are passed into thepropeller mixer 46 where they are thor-. oughly agitated, therebyeffectively contacting the hydrocarbon with the sodium bicarbonatesolution. The pH of the bicarbonate solution is about 7.8. From thepropeller mixer the-mixture of oil and aqueous phase are continuouslyled'through a line 48 to a settler 49 where the mixture separates into ahydrocarbon and aqueous phase.

The aqueous basic solution neutralizes the small amount of sulfuric acidcontained in the hydrocarbon without significantly saponifying thenaphthenic acids, thereby retaining the naphthenic acids in a form thatdoes not create a permanent haze when the oil is subsequently contactedwith water. Naphthenic acids per so are not a contributory factor to theformation of the haze. The separated aqueous phase is removed from thebottom of the settler 49 through the aforementioned recycle line 45which has placed within it a pump 50. Fresh aqueous sodium bicarbonatesolution by weight sodium bicarbonate) is added to the stream of therecycle line 45 in an amount of 4 parts per volume per hour. A smallamount of the spent solution is removed via a line 52 to maintain thecirculating volume. The added fresh sodium bicarbonate solution entersthe recycle line 45 through a make up line 54 under the pressure of apump 55.

The separated gas oil layer leaves the settler 49 through a line 57 to acoalescer 58 and from there passes to a settling tank 59 disposedimmediately below the coalescer. In the latter tank, a further quantityof the aqueous sodium bicarbonate solution is separated from the oil andreturned through a line 60 to the previously mentioned recycle line 45.

The gas oil from the top layer of the settling tank 59 moves through atransfer line 62 to a fourth propeller mixer 63. Water is added in aquantity of 50 parts by volume per hour to the sodium bicarbonatetreated hydrocarbon stream at a point preceding the mixer through a line65 under the pressure of a pump 66. The hydrocarbon and wash waterstream is thoroughly mixed and agitated in the mixer 63 and from therethe mixture is transferred via a line 68 to a settler 70 where the wateris separated from the gas oil and withdrawn from the bottom of the tankthrough a line 71. 'The washed gas oil leaves the settler through a line72 and is passed to a salt filter 73. From the latter unit thesubstantially dehydrated petroleum product is drawn off in the quantityof 485 parts by volume per hour through a conduit 75. A salt solution isremoved from the filter 73 via a line 76.

The data in Table I show the properties of the untreated feed, of theproduct, and of the hydrocarbon at various stages of processing. Thedata appearing in the far right hand column pertain to the treatedproduct, following water washing and drying. The latter two steps ofwater washing and drying are desirably included in the practice of theprocess but are not necessary. It will be seen that the oil from thecaustic solution treatment and prior to the acid treatment and sodiumbicarbonate wash develops a permanent haze on contact with water.However, the completely processed product remains wholly clear to likehandling. Moreover, as a result of the treatment, the content of thenitrogen bases is also very much reduced and there results a significantreduction in the mercaptan sulfur content. The acid number valueappearing in the fourth column under the heading After Acid Treatment isprincipally attributable to the presence of mineral acid.

Table I Feed After After After Sodium Vene- Caustic Acid Bicarbonatezuelan Solution 'lreat- Treatment, Gas Oil Treatment ment Water Wash AndDrying Sulfur content 1.63%... Acid Number, mg 2.83".-- 0.02003...0.1-0.2... 0.04.

KOFl/g. Ash content, percent 0.018.--. 0.001-. 0.001.

w Mertcagtans, percent 0.0021-.. 0.0020..-.- 0.0004... 0.0004.

w Nitrogen bases calcu- 121 121 5 5.

lnted as parts by wt. N per million parts by wt. oil. Union color 2min..- 1 min. Union color after 24 h. 7 min... 2 min.

heating to C. in the presence of iron. Odor Good.... Offensive Good.Appearance of the gas Perma- Completely oil after shaking with nentclear. water, followed by haze. hour centrifuging.

We claim as our invention:

1. In a process for refining a petroleum hydrocarbon mixture containingnaphthenic acids, sulfur compounds and nitrogen bases wherein there is amixing of the hydrocarbon with an aqueous alkali wash solution wherebythe naphthenic acids are converted to water-soluble soap and whereinthere is a separation of the mixture of hydrocarbon and wash solution toobtain a washed hydrocarbon phase containing a small amount ofnaphthenic soaps and an aqueous wash phase containing the remainder ofsaid soaps, the improvement comprising treating the alkali-washedhydrocarbon with an excess of sulfuric acid to remove nitrogen bases andto acidify the naphthenic soaps contained therein and subsequentlywashing the acid treated hydrocarbon containing excess sulfuric acidwith an aqueous basic solution of a salt of a Weak acid and a strongbase, saidsolution having a pH of less than 8.5, to neutralizesubstantially the sulfuric acid remaining therein from the acidtreatment without significantly saponifying the naphthenic acids to theextent that they form a permanent haze when the oil is contacted withwater.

2. A process in accordance with claim 1 wherein the aqueous basicsolution contains sodium bicarbonate present in the amount of betweenabout 15% by weight of the solution.

3. A process in accordance with claiml wherein the aqueous basicsolution contains sodium acetate present in the solution in an amountbetween approximately 15% by weight. g a

4. A process in accordance with claim 1 wherein the aqueous basicsolution contains a salt of a weak acid and a strong base present in anamount between about 15% by weight of the solution and wherein 10-50parts by volume of said solution are employed to washabout 100 parts byvolume of the hydrocarbon.

References Cited in the file of this patent UNITED STATES PATENTS1,317,582 Knottenbelt Sept. 30, 1919 1,605,046 Maitland Nov. 2, 19261,761,328 Chappell June 3, 1930 1,823,614 Lemmon Sept. 15, 19312,112,313 Sowers Mar. 29, 1938

1. IN A PROCESS FOR REFINING A PETROLEUM HYDROCARBON MIXTURE CONTAININGNAPHTHENIC ACIDS, SULFUR COMPOUNDS AND NITROGEN BASES WHEREIN THERE IS AMIXING OF THE HYDROCARBON WITH AN AQUEOUS ALKALI WASH SOLUTION WHEREBYTHE NAPHTHENIC ACIDS ARE CONVERTED TO WATER-SOLUBLE SOAP AND WHEREINTHERE IS A SEPARATION OF THE MIXTURE OF HYDROCARBON AND WASH SOLUTION TOOBTAIN A WASHED HYDROCARBON PHASE CONTAINING A SMALL AMOUNT OFNAPHTHENIC SOAPS AND AN AQUEOUS WASH PHASE CONTAINING THE REMAINDER OFSAID SOAPS, THE IMPROVEMENT COMPRISING TREATING THE ALKALI-WASHEDHYDROCARBON WITH AN EXCESS OF SULFURIC ACID TO REMOVE NITROGEN BASES ANDTO ACIDIFY THE NAPHTHENIC SOAPS CONTAINED THEREIN AND SUBSEQUENTLYWASHING THE ACID TREATED HYDROCARBON CONTAINING EXCESS SULFURIC ACIDWITH AN AQUEOUS BASIC SOLUTION OF A SALT OF A WEAK ACID AND A STRONGBASE, SAID SOLUTION HAVING A PH OF LESS THAN 8.5, TO NEUTRALIZESUBSTANTIALLY THE SULFURIC ACID